1. Field of the Invention
The invention is in the field of signaling and specifically in the field of traffic control using signal lights.
2. Background
FIG. 1 illustrates a prior art traffic signal 100 typically including three or more lamps 110A-110C. In a standard format these lamps are co-linear, shine with distinguishable colors red, yellow, and green, and display a filled circle pattern. When mounted vertically the red lamp is by convention (in the United States) located above the yellow and green lamps. As shown in FIG. 2A, each lamp 110 includes a single bulb 210 or alternatively, as shown in FIG. 2B, a series of bulbs 220 such as LEDs (light emitting diodes). Lamp 110 may also includes an optional lens (not shown) that modifies the apparent color of a bulb 210 or series of bulbs 220. For example a red lamp 110 may have a red lens that makes light from the lamp appear red in color.
Lamp 110 optionally has a pattern (mask or shape) that forms a pattern meaningful to traffic control, such as an arrow or a default filled circle pattern, in a lit surface. FIG. 3 illustrates four of these patterns, in addition to the default filled circle pattern, having different meaning to traffic control. An arrow pattern 310 is used for directional control. A bar pattern 320 and a xe2x80x9cTxe2x80x9d pattern 340 are used to control rail traffic. A cross pattern 330 is used in a variety of applications such as traffic direction control. Each pattern is rotated to other orientations and is used with a variety of colors. Both pattern and color determine the function of an individual lamp 110 meaningful to traffic control.
FIGS. 4A through 4C illustrate variations of prior art traffic signal 100. Advanced traffic signal 410 includes a green lamp 440 with an arrow pattern 310 used for direction control. In the figures, lamp 110, not showing a specific pattern, are meant to illustrate a default filled circle pattern. Advanced traffic signal 420 includes a yellow lamp 450 with arrow pattern 310 used for direction control. Advanced traffic signal 430 includes a red lamp 460 with a cross pattern 330 and a green lamp 440 with an arrow pattern 310 rotated ninety degrees. Advanced traffic signal 430 is used for lane control. Advanced variations of traffic signal 110, such as those illustrated, can include three or more lamps. A large number of lamp 110 in traffic signal 100 is a disadvantage. Each lamp 110 contributes to the cost and weight of traffic signal 100. Prior art lamp 110 does not have variable patterns that allow an individual lamp to provide variable information meaningful to traffic control displays. For example as a signal cycles through a display pattern, wherein alternative lamps are lit, a light pattern on an individual lamp cannot be changed from a default filled circle pattern to an arrow pattern 310 of the same color. Lamps 440, 450, and 460 are variations of lamp 110.
Prior art traffic signals are supported by supporting elements such as poles and cables. The weight of the traffic signal is a factor in the requirements and, therefore, cost of the support elements. In a typical installation several traffic signals are supported by one or more supporting elements and coupled through a single control module including electronics.